Black and Bruised Toenails: A Runner’s Guide to Toenail Injury Prevention Written by John Davis - Get free updates here

Anyone who’s ever run a tough, hilly race or long run more than a few times, especially on trails, can probably guess what “jogger’s toe” refers to.

The black, bruised appearance of one of your toenails after it takes a beating during a run is accepted by some runners as an integral part of running, but these bruised toenails can cause problems if left unchecked.

Injured toenails are not only painful and an ugly sight to look at, but can end up infected as well—the warm, moist environment inside your shoes is the perfect home for bacteria.

This week, we’ll be looking through the scientific literature for the causes of and treatments for jogger’s toe.

Statistics on toenail injuries in runners

One survey of participants in a 1973 marathon reported that 14% of the runners suffered blisters, chafing, or loss of toenails that persisted for at least a week after the race. A later study at the London Marathon found that only a few of the runners (0.1% total) treated at aid stations had toenail problems.

Both of these studies have their limits, of course, since a toenail problem alone is probably not serious enough to warrant a stop at an aid station, and subjects in the first study were probably more apt to respond to the survey if they’d suffered toe or skin problems.

The true prevalence of toenail injuries in long-distance runners is probably somewhere in between these percentages, and is likely dependent on the distances and terrain that individual runners cover in their training and racing.

Toenail injury causes

According to a 2004 review article by E.A. Mailler and B.B. Adams, the cause of toenail injuries during running is rooted in the repeated impacts that occur with each step. After the initial impact with the ground, there is a brief moment where your shoe has come to a stop but your foot inside of it has not. Your foot slides forward, usually only by a small amount, but this causes your toenails to take the brunt of the impact with the toebox of your shoe. Additional stress is applied to your toenails when you push off from the ground, as your toes “claw” at the ground to gain additional propulsion.

As you might suspect, poorly-fitted or loosely-laced shoes can exacerbate the problem: a shoe without sufficient room for your foot to slide forward will cause a more abrupt impact at your toenails, and a shoe with a toebox that is too low will push down on the top of your nails as you push off the ground. Shoes that are laced too tight can compress the toenails as well, but conversely, a shoe that isn’t laced tightly enough will allow your foot to slide too far forward, banging your nails against the front end of the shoe.

Downhills also magnify the problem, since they increase your speed and vertical impact force (and hence the momentum of your foot as it is sliding forward) as well as slanting your shoe downward, creating a ramp for your foot to slid down.

Finally, longer runs and longer races obviously are more prone to cause problems with your toenails, since each step leads to additional stress on the nail. The gradual swelling in your feet that occurs after you’ve covered many miles doesn’t help either, as it effectively reduces the size of your shoe. Given all of the factors at play, it’s not hard to see why ultramarathoners, who often do 20 or 30-mile runs over hilly trails, are renowned for their ugly toenails.

Mailler and Adams claim that the toes most commonly affected are the longest ones: the big toe, the second toe, and the third toe. The relative lengths of these individual toes depends on the person, so if you have what’s sometimes called an “Egyptian foot” (where your big toe is the longest), you will likely get blackened and bruised toenails on your big toe, whereas if you have a “Greek foot” (with either the second or third toe being the longest), these toes are more likely to get injured.

Keys to prevention of black and bruised toenails

Mailler and Adams authored a later review of skin conditions in runners which detailed treatment and prevention options for jogger’s toe.

Keeping your shoes laced snug, but not too tight, and making sure the toebox is large enough to keep pressure off of your nails, even after extended periods of running where your feet have swelled up a bit.

Using an “ankle lock” lacing to secure your foot in the shoe can also be helpful, as it reduces the distance your foot slides inside of your shoe on footstrike.

Keeping your toenails trimmed short and square (not curved) will also help evenly distribute stress on your toe. If you’ve already got a blackened and bruised toenail, you can leave it alone if it isn’t bothering your running. If it is, you can try soaking in warm water to relieve some of the irritation.

According to Mailler and Adams, draining the fluid under the nail—either by puncturing the nail itself with a hot needle or draining it from the front, underneath the toenail—is somewhat controversial, as it can increase the risk of infection, but can nevertheless prevent the problem from getting worse, or losing your toenail entirely (which is not as bad as it sounds).

Finally, you should be aware that some other skin and foot problems can masquerade as jogger’s toe. Onychomycosis (or simply ringworm), a fungal infection of the nail, can also cause a toenail to appear discolored and bruised. While it can be treated, albeit with some difficulty, as the fungus is embedded within the nail itself, it does need to be positively diagnosed by a doctor or, preferably, a podiatrist.

Additionally, melanoma, a serious cancer of the skin, can manifest underneath the toenails as well, making it sometimes hard to distinguish from a bruised toenail.

If your jogger’s toe doesn’t seem to be improving, or if it appears infected and swollen, you should see a doctor before the problem gets any worse. Jogger’s toe can be an annoyance, but if you take care of your feet and make sure your shoes fit right, it doesn’t have to slow you down.

But seriously, you mentioned this under prevention, but “untrimmed nails” could also be listed under a cause.

I also recently lost a nail due to a very long run in a new and apparently too small pair of yaktrax. They were just too tight and squeezed the shoe a bit, after 2 hours I just took them off and carried them.

I recently switched from wearing a Nike Flex Run to a Nike Free Run and after a few weeks I have just started developing a bruised toenail on my right big tow. I have been running consistently for the past year, about 3-4 times a week and 4 miles per run. I have never had a problem with my toe until after switching to a new pair of shoes. I think the toe box is narrower and maybe has less volume. I hasn’t really bothered me much until today, which has been my 7th or 8th run in the new Nike Free. What’s your take on this? I spent 100 bucks on the new shoes so I would hate to have to ditch them and shell out more money again, but if that’s what it takes to continue running then so be it.

i switched to Nikis. Noticed it had a narrow. I spent 4 months trying to break them in. My feet are bruised and battered. The nail on my little toe is infected. Not worth it. I’m on antibiotics to cure the infection. The nail will fall off later. Get rid of those shoes or you might suffer from them later.

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About the Author

John Davis
is a recent graduate of Carleton College and a long-time student of distance running. Currently, John has immersed himself in scientific research on physiology and biomechanics, trying to answer questions like "why do runners get injured?" and "how does training improve fitness?"